Results from a round of feedback with Bharat.

Squashed commit of the following:

commit 13dbd3515bfb5324cfbcb3bbeafc179771b54f75
Merge: f0f094c 97400b7
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 20:33:02 2011 -0600

    Merge branch 'master' of https://github.com/gallery/gallery3 into rawphoto

commit f0f094c3f79b09536f58083681c28f73271c506d
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 20:22:49 2011 -0600

    Explain the conditional rename in item::save() with a comment.

commit 1b3a6b85c156e4777d2aa8205b130984f55dc66d
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 18:29:34 2011 -0600

    Improve the comment explaining why the data_file extension is important.

commit c3e8c1e3b5e3cb1046acd4c923bb0ae9dbcd603a
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 18:12:56 2011 -0600

    The data_file field is public, so we don't need to supply an accessor method.

commit 2375a02e2cdbd1ccaf7dc4d3db9d85119972e3a9
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 16:40:55 2011 -0600

    Change the signature of system::tempnam to something more appropriate for Gallery.

commit a8ca9dcf9edd54633c0c78b3af76aa974d38fc64
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 16:10:06 2011 -0600

    Change the name of the extensions helper to legal_file.

commit 7e61a01a96f5eab7212dba754ac64fdfb4d9e8ab
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 30 16:08:49 2011 -0600

    Change the name of the extensions helper to legal_file.

commit 4c2b2ebd3f2052898fbfb175650ed4cf49c8006e
Author: Chad Parry <github@chad.parry.org>
Date:   Wed Apr 27 20:52:35 2011 -0600

    Remove a newline at the end of the file that I accidentally introduced.

commit 6d564f185e5279d6cca9a7385066514ff18a2455
Merge: 7ff485f 4060640
Author: Chad Parry <github@chad.parry.org>
Date:   Wed Apr 27 20:35:58 2011 -0600

    Merge branch 'master' of https://github.com/gallery/gallery3 into rawphoto

commit 7ff485fa48c392bbbb0370f67cb1bd6fcc00c2a4
Author: Chad Parry <github@chad.parry.org>
Date:   Wed Apr 27 20:29:06 2011 -0600

    Move the extensions helpers out of the Kohana system directory and into their own Gallery Extensions class.

commit 26585fed03236f0f70a75959e1d3002025f4e15e
Merge: 809567f c8f90e8
Author: Chad Parry <github@chad.parry.org>
Date:   Sun Apr 24 08:28:39 2011 -0600

    Merge branch 'master' of https://github.com/gallery/gallery3 into rawphoto

commit 809567f12850f59bdeb47a2963f6968b99b5a201
Author: Chad Parry <github@chad.parry.org>
Date:   Sun Apr 24 08:10:04 2011 -0600

    Expose the data file field.

commit fcb06bf175bb9eeff36d9c294e97ace9374ef0f3
Author: Chad Parry <github@chad.parry.org>
Date:   Sun Apr 24 00:45:12 2011 -0600

    Don't assign to the item->name field if the name is unchanged, because the save method will crash.

commit c6ef706d70c7e48bea1145eec1b13fb5683e023f
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 23 22:55:59 2011 -0600

    Preserve old data files long enough for them to be available to event handlers.

commit 0d6a3a3cfc4f38f450db9e18da47a5e2ad826af8
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 23 21:19:47 2011 -0600

    Create a tempnam substitute that safely creates files with a given extension.

commit e149cf7238a1f8eaddfc68580f2d636dd8255795
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 23 16:39:25 2011 -0600

    Support data files that change their extension and MIME type.

commit 6702104f571413e4d57db3515b2070c48d3e9b55
Author: Chad Parry <github@chad.parry.org>
Date:   Sat Apr 23 16:35:00 2011 -0600

    Resolve an infinite recursion that happens when the path caches are updated during saving.

commit 944cb72eea946f4c45a04b7e4c7c33929fa8b9f3
Merge: 567522b 5af74d4
Author: Chad Parry <github@chad.parry.org>
Date:   Fri Apr 22 14:10:42 2011 -0600

    Merge remote branch 'origin/master' into rawphoto

commit 567522bfa08c370bb5baf8454afc5b04bc9e49b4
Author: Chad Parry <github@chad.parry.org>
Date:   Thu Apr 21 20:12:32 2011 -0600

    Add an event for when a new graphics toolkit is chosen.

commit 31ba081b793141ca36866a6dd349cd2eac5af68e
Author: Chad Parry <github@chad.parry.org>
Date:   Thu Apr 21 02:06:53 2011 -0600

    Add an event that will collect all valid filename extensions.

1 files changed, 39 insertions, 0 deletions

diff --git a/modules/gallery/helpers/legal_file.php b/modules/gallery/helpers/legal_file.php
new file mode 100644
index 00000000..2cb0fb25
--- /dev/null
+++ b/modules/gallery/helpers/legal_file.php
@@ -0,0 +1,39 @@
+<?php defined("SYSPATH") or die("No direct script access.");
+/**
+ * Gallery - a web based photo album viewer and editor
+ * Copyright (C) 2011 Chad Parry
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+class legal_file_Core {
+  static function get_extensions() {
+    // Create a default list of allowed extensions and then let modules modify it.
+    $extensions_wrapper = new stdClass();
+    $extensions_wrapper->extensions = array("gif", "jpg", "jpeg", "png");
+    if (movie::find_ffmpeg()) {
+      array_push($extensions_wrapper->extensions, "flv", "mp4", "m4v");
+    }
+    module::event("legal_file_extensions", $extensions_wrapper);
+    return $extensions_wrapper->extensions;
+  }
+
+  static function get_filters() {
+    $filters = array();
+    foreach (self::get_extensions() as $extension) {
+      array_push($filters, "*." . $extension, "*." . strtoupper($extension));
+    }
+    return $filters;
+  }
+}